The present invention relates to a metal gasket with a fluid hole sealing device, to which different tightening pressure is applied when a gasket is tightened.
In an internal combustion engine, there are provided many holes, such as cylinder bores, water holes, oil holes, push rod holes, bolt holes and so on. In these holes, a large combustion force or pressure is created at the cylinder bores, while a moderate force or pressure is applied to the water holes and other holes.
Since the large combustion force is created at the cylinder bores, the bolt holes are arranged to effectively seal around the cylinder bores. The other holes are arranged properly around the cylinder bores. Therefore, areas around the cylinder bores are relatively equally pressurized by the bolts to securely seal around the cylinder bores when the gasket is tightened. However, areas around the other holes are not equally pressurized when the gasket is tightened.
In a cylinder head gasket, in order to provide a strong surface pressure around the cylinder bore when a gasket is tightened, in case a bead is formed around the cylinder bore, a bead for forming a high surface pressure is formed around the cylinder bore. Also, the area around the cylinder bore may be made thicker than an area outside thereof to provide a high compression pressure thereat.
Therefore, when the gasket is installed in the engine and is tightened by the bolts, the cylinder head may be curved such that a portion corresponding to the cylinder bore slightly extends outwardly or upwardly. Therefore, equal surface pressure is not formed at, especially, an area around a water hole near the cylinder bore when the gasket is tightened.
In addition, when an engine is operated, the engine vibrates and is heated at high temperatures. Accordingly, it is liable to leak from other holes.
In view of these problems, there have been proposed many methods. For example, in case a gasket is provided with a bead around a hole to be sealed, a pressure regulation plate or portion is formed adjacent to the bead so that the bead is not completely compressed when the gasket is tightened to thereby prevent creep relaxation of the bead.
In U.S. Pat. No. 4,759,556, a portion away from the bolt is generally weak in surface pressure when the gasket is tightened, so that one bead is separated into two beads at the portion away from the bolt to provide strong surface pressure thereat when the gasket is tightened.
In Japanese Patent Publication (KOKAI) No. 62-155375, a bead is formed around a cylinder bore such that a portion of the bead away from the bolt hole has large spring constant to provide equal surface pressure on the bead when the gasket is tightened.
In the prior art, a part of a bead is formed to provide strong surface pressure when the gasket is tightened. In this case, when the bead is strongly tightened, the bead may be compressed properly. However, in case a strong tightening pressure is not applied, large surface pressure is not formed at the portion away from the bolt. Therefore, leakage may happen at that portion.
Accordingly, one object of the present invention is to provide a metal gasket with a fluid hole sealing device, which can seal properly at a portion where equal tightening pressure is not obtained.
Another object of the invention is to provide a metal gasket as stated above, which can effectively seal around the fluid hole for a long period of time.
A further object of the invention is to provide a metal gasket as stated above, which can be easily and economically manufactured.
Further objects and advantages of the invention will be apparent from the following description of the invention.